The early Holocene deglaciation of the Laurentide Ice Sheet (LIS) is the most recent
and best constrained disappearance of a large Northern Hemisphere ice sheet. Its
demise is a natural experiment for assessing rates of ice sheet decay and attendant
contributions to sea level rise. Here we demonstrate with terrestrial and marine
records that the final LIS demise occurred in two stages of rapid melting from ~9.0-
8.5 and 7.6-6.8 kyr BP with the LIS contributing ~1.3 and 0.7 cm yr-1 to sea level
rise, respectively. Simulations using a fully coupled atmosphere-ocean general
circulation model suggest that increased ablation from enhanced early Holocene
boreal summer insolation may have been the predominant cause of the LIS
contributions to sea level rise. Although the boreal summer surface radiative
forcing of early Holocene LIS retreat is twice that of projections for 2100 C.E.
greenhouse gas radiative forcing, the associated summer surface air temperature
increase is the same. The geologic evidence for rapid LIS retreat under a
comparable forcing provides a prehistoric precedent for a possible large negative
mass balance response of the Greenland Ice Sheet by the end of the coming century.

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dc.description.sponsorship

This research was funded by
National Science Foundation grants ATM-05-01351 & ATM-05-01241 to D.W.O. &
G.A.S., start-up funds from the University of Wisconsin-Madison and a Woods Hole
Oceanographic Institution Postdoctoral Scholarship to A.E.C., and the Woods Hole
Oceanographic Institution's Ocean and Climate Change Institute (D.W.O. & R.E.C.).